As I said before I can't  render a pdf document with a relative url inside like css files. 
* Why ? Because this method needs to render the page with an absolute path. But the route I used  is not directly accessible. It is behind a Symfony firewall and accessible only the owner of the invoice.
* The impacts : 

=> I can not have CSS like 

```html
<link media="print" type="text/css" href="/assets/compiled/frontend_print.css" rel="stylesheet">
```
  =>  this means I can not use something like

```php
{% stylesheets output='assets/compiled/frontend_print.css'
            '//netdna.bootstrapcdn.com/twitter-bootstrap/2.3.2/css/bootstrap-combined.no-icons.min.css'
            '@SyliusWebBundle/Resources/assets/css/print.css'
%}
    <link rel="stylesheet" href="{{ asset_url }}" type="text/css" media="print" />
{% endstylesheets %}
```

I feel a little bit stuck. I agree rendering the CSS directly inside this template is far to be perfect. But is this that serious ? Not sure ^^